1. Technical Field
The present invention relates to a liquid ejecting head and a liquid ejecting apparatus having the same, and particularly, to a liquid ejecting head and a liquid ejecting apparatus having the same that are suitable to apply when separating and circulating a part of liquid that is discharged from a pressure generating chamber and ejected through a nozzle opening.
2. Related Art
As a liquid ejecting apparatus, for example, there is an ink jet type recording apparatus provided with an ink jet type recording head including: a plurality of pressure generating chambers that generate pressure for ejecting an ink droplet by a pressure generating unit formed of a piezoelectric element; an ink supply channel that individually supplies the ink from a common reservoir to each pressure generating camber; and a nozzle opening that ejects the ink droplet formed in each pressure generating chamber (for example, refer to JP-A-2002-355961).
In the above-described ink jet type recording apparatus, ejecting energy is applied to the ink in the pressure generating chamber that is communicated with a nozzle corresponding to a printing signal, and the ink droplet is ejected from the nozzle opening to the outside and landed at predetermined positions on media such as a sheet. Therefore, in this kind of ink jet type recording apparatus, the nozzle opening is exposed to the atmosphere. Thus, the ink is thickened due to vaporization via the nozzle opening. As a result, the thickened ink may cause an adverse effect on ejecting characteristics of the ink droplet. That is, if the thickened ink exists at even a portion of the nozzle opening, ejection amount and an ejection speed of the ink droplet through the nozzle opening are changed, and disadvantages such as variation in the landing of the ink occur.
Therefore, the versatile ink jet type recording apparatus according to the related art includes the following methods: 1) before the ink is thickened, the ink jet type recording head is moved to portions other than the media, and the ink in the vicinity of the nozzle opening is always maintained to a fresh state by discharging the ink appropriately; or 2) when the ink droplet is not ejected, vibration is generated at the pressure generating chamber by PZT or the like serving as the pressure generating unit and the thickening of the ink is suppressed to some extent.
However, the versatile ink jet type recording apparatus according to the related art has the following problems. That is, in the case of the above-described 1), the ink is uneconomically discarded, and in the case of the above-described 2), even when the ink is vibrated, it is difficult to prevent sufficiently the ink from thickening due to vaporization of the ink in the vicinity of the nozzle opening.
Therefore, there is also proposed an ink jet type recording head constituted so that a part of ink discharged from the pressure generating chamber and flowed toward the nozzle opening is separated and circulated through a flow channel for circulation, and fresh ink is always supplied to the vicinity of the nozzle opening (Japanese Patent No. 3097718). In the ink jet type recording head adopting the above-described circulating method, since the ink is circulated, the ink in the vicinity of the nozzle opening can be always maintained at a fresh state without discarding the ink and problems of the above-described 1) and 2) can be simultaneously solved.
On the other hand, in the ink jet type recording head adopting the above-described circulating method, since a part of the ink flowed toward the nozzle opening is separated through the flow channel for circulation, the amount of the ink ejected through the nozzle opening is decreased by as much as the separated amount. Therefore, the discharging efficiency of the ink with respect to an excluded volume of the ink is decreased in the pressure generating chamber. That is, in the above-described ink jet type recording head adopting the circulating method, it is very important to obtain the same ejecting characteristics as that of the versatile ink jet type recording apparatus of the related art which does not adopt the circulating method. However, a technology or the like for obtaining the same ejecting characteristics have not yet achieved.
In addition, the above-described problems exist similarly not only in ink jet type recording heads that eject the ink but also in liquid ejecting heads that eject other liquids.